This invention relates generally to nuclear reactors, and more particularly, to a passive aerosol retention device for reducing the offsite radiation dose resulting from particulate aerosols during a severe accident.
One known boiling water nuclear reactor includes a reactor pressure vessel and a primary containment vessel. The primary containment vessel includes a lower, an upper drywell, and a passive containment cooling system. The upper drywell is separated from the lower drywell by the reactor pressure vessel skirt and support. Circular vents permit communication between the lower and upper drywells. The primary containment vessel surrounds the reactor pressure vessel and can withstand pressure generated by the reactor pressure vessel during reactor accident conditions and to contain any radioactive aerosols that may be generated during a severe accident condition. Particularly, the reactor pressure vessel is positioned within the primary containment vessel, which contains pressure resulting from accidents including a Loss-Of-Coolant Accident (LOCA), and severe accidents.
During a theoretical case of a severe accident, interactions of the corium with structural materials may cause the generation of radioactive aerosols, primarily in the lower drywell. These aerosols are subsequently transported into the upper drywell through the connecting vents by a steam and non-condensable gas flow. Recirculatory flows between the upper and lower drywell tend to distribute the aerosols between the upper and lower drywells. A certain percentage of the aerosols are retained in the upper drywell due to agglomeration and deposition on the containment surface. A portion of the aerosols are transported to the suppression pool via the passive containment cooling system. Some of the insoluble particulate aerosols deposit in the tubes and headers of the passive containment condenser (PCC) unit, thereby degrading the PCC heat removal capability and the overall containment heat removal performance.
Another portion of the aerosols in the upper drywell escape via leakage paths which may develop during a severe accident. The leakage of aerosols from the containment vessel is an important contributor to the offsite radiation dose. In addition, a resuspension of the aerosols agglomerated and deposited on the containment walls and in the PCC tubes and headers may occur which have an effect on the aerosol concentration in the upper drywell.
It would be desirable to provide a mechanism to minimize the offsite radiation dose and improve containment heat transfer capability during a severe accident by reducing the aerosol concentration in the upper drywell.